Electrical conductor



N 19, 1940- w. c. ROBINSON ETAL 2,222,555

ELECTRICAL CONDUCTOR Filed Dec. 27, 1937 A TTORNEYS.

' Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE ELECTRICALCONDUCTOR William C. Robinson, Sewickley, and Ralph W. E.

Moore, Mount Lebanon, Pa.; said Moore assignor to said RobinsonApplication December 27, 1937, Serial No. 181,910 Claims. (Cl. 174-120)This invention relates to electrical conducturns of the wrapping tend tobecome separated, tors of the types having an inner electrically inandto unwind and loosen when the conductor is sulated conductive structureand employing an flexed, due to deformation of the flexible dielecouterprotective jacket of fibrous material. Extric. It has been proposed tohold the turns of 5 amples are rubber covered wire used as building awrapping of this sort by means of threads in- 5 wire or as theindividual wires of various types serted between the wrapping and thedielectric, of cable, such as flexible armored cable or mom or stitchedunder and over groups of turns of metallic sheathed cable. Such jacketsare the wrapping. Aside from the manufacturing usually coated withsaturating and covering comdifficulties which such structure presents,it does pounds. The present invention deals with the not fully solve theproblem of protecting the con- 10 structure of the jacket. rather thanwith the c r in ll direc i n of fl xi n a i the coating, which may be ofany suitable sort. tendency for turns or groups of turns to open up.

. It is our purpose to provide electrical conduc- It a been proposedalso to hold the serving tors of the insulated type which arefundamenintact by means of saturating compounds and tally simple, andwhich are substantially equivathe adhesive effect of vulcanizing therubber in- 15 lent in character to the present types of consulation bythe heat of the saturating bath. ductor assemblies which include braidedor knit- While this has some effect, it is not sufilcient to tedcoverings; which conductors are flexible, are m h r q r e t of w rkinditions unsecurely and permanently organized, and which 8 Which a WifeCable must be t Severely may be manufactured with a maximum of opand y tm nt t i e l S ructure. 20 erating convenience and speed. We have foundthat an improved outer protec- In manufacturing insulated conductorsadapttive jacket can be made by combining such a ed when so desired to amoisture-resistant e cal Servi g of thread, having its. turns laidand/or flame-resistant treatment and adapted close together with asubstantial lead and withuniversally to use in cables or in housed orun- Out Overlap to form 8 Closed W pp g r Jacket 25 housed installation,it is necessary that the ingiving ub t nt a y Complete Coverage, with ansulated conductor itself be adequately flexible open locking structureof thread oppositely and that the insulation surrounding theconclucwound upon the jacket, the turns of thread in tive element of theassembly be so organized that this locking Structure being Spaced apartto K- all its constituents remain in their initial arp s th r at r partof t e ia k tso rangement in the assembly. Simplicity in the Thislocking Structure fi i y Prevents e assembly both as to the number andarrangeserving threads from opening up when the conment of itsconstituent elements is a matter of ductor is bent. t us olding theServi g intact.

'. "primary importance, and the problem is to join A o g t locking S u ue ies outside this simplicity with manufacturing facility and t eServing, the effect of the sp of i turns 35 permanence of organization.is such that it brings about no material increase In attaining ourobject a flexible conductive in the over-all diameter of the wire orcable. element, which may be either a single conductor The effectivediameter for practical purposes is wire, or a plurality of the same, isencased in a fixed by the serving and whatever saturant or 40 flexible,directly applied dielectric material, such Coating is pp to d 8 958 t anhe di 0 as a rubber composition or a composition having ameter of awireor cable similar in other respects electrical and physical qualitiessimilar to those but e ploying the usual braid. An outer jacket ofrubber. The term flexible as herein apso formed is flexible, givesbetter coverage and plied to the conductive metallic element of theconsequen better p c ion than the convenconductor is used in its commonand non-techtiohal b d. is e rapi ly pp a d, whe 45 nical sense, asmeaning merely capability to be coated in the usual way, presents a goodsurface flexed. This flexible dielectric about the com for printing andoflers less resistance to being ductive element of the assembly iscovered with pul ed when the wire or cable is fished into conaprotective jacket in the form of a wrapping of duits or drawn throughholes in beams and the thread, such for example as cotton, or paper,like. e

thread. Great manufacturing advantage is de- In the accompanyingdrawings, Fig. 1 i a rived by applying this thread in the form of aview, chiefly in elevation but partly in longitudisimple helicalwrapping called a serving rather nal section, showing our conductorassembly as than in the form of a braided or knitted fabric. organizedwith a single locking thread. Fig. 11

When applied asasimple wrapping, however, the is an elevatlonal viewshowing our conductor 55 assembly organized with two locking threads.Fig. III is a view, taken in elevation, showing a conductor assembly inwhich a plurality of wrapping threads have been simultaneously woundwith a simple helical lay.

In describing the insulated conductor of our invention, it should beexplained that the simple conductor, such as is shown in the drawingsforms one assembly in which our invention resides, and coherence andflexibility are the desired qualities of this conductor as such. vMerely as shown, the conductor may, if so desired, be used in manyelectrical associations. The conductor as such may for some purposes,such as for use in housing and conduits, or for use in armored cable, beprovided with a coating of suitable moisture-repellent composition whichis also desirably flame-resistant and many include a superficial waxfinish as described in Patent No. 1,635,829, the whole forming aflexible protective coating, the makeup of which is not a part of thisinvention. It may be used in making up non-metallic sheathed cable, orsuch as the cable shown and described in Frederickson United StatesPatent No. 1,687,013, and may be used as the conductor in various otherorganizations. It is, therefore, the qualities of flexibility,simplicity, and permanent organization in the fundamental structureshown, which are the results under consideration, without reference toadded structure, or material, which may be associated with theconductor.

Referring to the drawing, in assembly the insulated conductor consistsof a flexible conductive element I, shown as a single conductor wire.The other core element of the assembly is a covering 2 of dielectriccomposition, such as rubber composition or a generally similarcomposition directly surrounding the conductive element. Around the coreof the assembly there is wound, with a simple helical lay, a wrapping I,the turns of which are in contact with each other longitudinally of thecore. This wrapping I is desirably laid with a number of individualthreads or ends, as they are called, giving a substantial lead in orderto increase the speed with which it may be applied to the core; andwhile it remains in the coherent condition shown, serves to confine andprotect the flexible dielectric material of the core.

In order so to bind the turns of the wrapping that they are held againstspreading by deformation of the flexible dielectric element when theconductor is flexed, we look the turns of wrapping thread in position bymeans of at least one looking thread 4 helically wound oppositely to thewinding of the wrapping, to lie wholly outside the wrapping and to crossthe turns of the wrapping thread while forming a substantial angle withthe longitudinal axis of the core. The angle formed with thelongitudinal axis of the core by the locking thread should besubstantial, to lessen likelihood that the thread may be broken underdisruptive forces exerted by the dielectric material of the assembly inflexion of the conductor. We prefer that the angle formed with thelongitudinal axis of the conductor by the locking thread should not besubstantially less than a 60 angle, having found that an angleapproximating 60 provides a maximum locking effect for the wrappingthread in all directions of flexion of the conductor, while resulting inminimizing breakage of locking thread when the conductor is subjected tosevere conditions of use.

In order to insure coherence of the conductor wrapping under allconditions of use, we find it desirable, although generally unnecessary,to employ one or more additional locking threads 4, all the lockingthreads being similarly wound upon the wrapping to form a reverse helixtherewith. Irrespective of the number of locking threads included in theassembly, these threads should be so laid that each forms a substantialangle with the longitudinal axis of the conductor core, as in the caseof a single locking thread, and find that the optimum arrangement issimilarly so to lay all the locking threads that they each form an angleof approximately 60 with the longitudinal axis of the conductor core.The loclring threads are throughout their turns spaced uniformly fromeach other, giving the effect of parallelism in their positioning.

Both the wrapping thread and the binding thread, or threads, may berapidly laid upon the core of the conductor, and are of such nature andarrangement that they do not unduly detract from the flexibility of thecore structure of the conductor. In this connection we have found thatas many as three or four locking threads, spaced in what is effectivelya position of parallelism with each other, are not detrimental from theviewpoint of flexibility. Desirably, the thread which forms the wrappingl is a flbre thread of moisture-absorbent character, such as cotton,linen, hemp, or paper thread. For either the wrapping thread, or thelocking thread, or threads, we have found that we may suitably employthread of any material which has adequately high strength with respectto its cross-section. By the word "thread we mean to include coherentfilaments of any suitable material as well as the tightly twistedfibrous structures comprising more than one strand, and which arecommonly designated as thread" or cord." Each turn of the locking bemultiple, that is, consist of strands, and as so organized is to to be asingle thread.

Fig. III of the drawings shows a conductor assembly in which a pluralityof wrapping threads 5 have been simultaneously applied. These threads,wound in multiple, have, however, a simple helical lay, corresponding tothat shown in Figs. I and II. The one or more locking threads 4 areidentical with the locking threads 4 of Figs. I and II.

As compared with braided or knitted conductor structures, the wrappedand locked covering of our invention is at least equally flexible asconductor assemblies made with braided or knitted coverings, and is ofsmaller diameter than a conductor assembly comprising a braided or knitcovering. It is to be understood that, if desired, a double wrapping maybe provided, with the thread or threads of the outer wrapp ng arrangedin a simple helical lay, with the turns lying side by side in thewrapping, and not in part crossing each other as in a braided or knitcovering. In such arrangement locking thread, or threads, are appliedsimilarly to the outer wrappings. Such double wrapping is analogous to adouble covering of braided or knitted fabric, and bears the samerelation .to it that the single locked wrapping shown and describedbears to a conductor comprising a single braided or knit covering. Asexplained above, our invention resides in the use of a layer of wrappingarranged in a simple helical lay, and with a locking thread, or threads,lying in an opposed helix wholly outside that wrapping, irrespective ofthe omission or inclusion of other structure in the conductor assembly.

Our conductor has been subjected to relatively severe tests, approved byunderwriters, in order to prove its ability to meet the demands ofservice. One such test, which it successfully passed, is a bending testin which the conductor is flexed at least six times on a radius equalonly to 1.5 times the external diameter of the conductor assembly. Nolocking thread was broken, nor turns of the wrapping thread opened undersubjection to this test. The conductor similarly has passed the kinktest. That test is to grasp the conductor at two points separated asubstantial distance from each other, and then to give the conductor aquick torsional twist. This done successively in both directions, sothat the kink, or localized projection from the normal line of theconductor, is formed both with and counter to the direction in which thewrapping of the conductor is laid.

The proper use of the locking thread has also a bearing on a suitabilityof the conductor, which is not immediately apparent. This indirectbearing is to increase the flame resistance of the conductor. Assumingthat the organization herein specifically described is treated firstwith an inflammable asphalt composition, and has outside the asphalt aflame-retardant coating, such as pitch, the flame-retardance isdependent upon the coherence of the outer coating. If the coatingmaterial of the conductor be softened by flame impingement thereon, itsbinding efiect on the wrapping of the conductor assembly is decreased.In the absence of a properly arranged locking thread, or threads, theturns of the wrapping thread open, and in so doing disrupt the coatingmaterial. This exposes the asphalt to the flame, and results indestruction of the insulation in that region of the conductor. By thearrangement of the locking thread, or threads, in our conductor it hasthe same flame-retardant qualities as a similarly treated conductorcomprising a knit or braided fabric.

We claim as our invention:

1. An insulated conductor structure having a flexible metallicconductive element, an inner insulating structure and an outerprotective jacket in the form of a filamentary insulating servingsurrounding the said metallic conductive element with the turns of saidserving lying against each other in a simple helical lay to form aclosed wrapping, and a locking filament laid in a 'helix opposite insense to the helix of the closed wrapping and disposed in the assemblyoutside and in contact with the said wrapping, said looking filamentbeing laid with its turns out of contact with each other in an openbinder structure and arranged each to form an angle approximately asgreat as with the longitudinal axis of the conductor.

2. An insulated conductor structure having a flexible metallicconductive element, an inner insulating structure and an outerprotective jacket in the form of a coherent filamentary insulatingserving surrounding the said metallic conductive element with the turnsof said serving lying against each other in a simple helical lay to terma closed wrapping, and a permanently integrant binder structure for thesaid wrapping consisting of a locking filament laid outside the closedwrapping with its turns out of contact with each other in a helixopposite in sense to the helix of the closed wrapping and forming a.substantial angle with the longitudinal axis of the conductor, the saidlocking filament being in direct contact with the said closed wrappingpositively to oppose and effectively to inhibit opening between thecoherent wrapping turns during fiexion of the conductor.

3. An insulated conductor structure having a flexible metallicconductive element, an inner insulating structure and an outerprotective jacket in the form of a coherent filamentary insulatingserving surrounding the said metallic conductive element with the turnsof said serving lying against each other in a simple helical lay to forma closed wrapping, and a locking filament permanently integrant for thesaid closed wrapping laid in a helix opposite in sense to the helix ofthe closed Wrapping and in position effectively to inhibit openingbetween coherent turns ofthe wrapping, said locking filament being laidwith its turns out of contact with each other in an open binderstructure and arranged each to form an angle approximately as great as60 with the longitudinal axis of the conductor.

4. An insulated conductor structure having a flexible metallicconductive element, an inner insulating structure and an outerprotective jacket in the form of a coherent filamentary insulatingserving surrounding the said metallic conductive element with the turnsof said serving lying against each other in a simple helical lay to forma closed wrapping, and a permanently integrant binder structure for thesaid closed wrapping consisting of a locking filament laid outside theclosed wrapping in a helix opposite in sense to the helix of the closedwrapping and with its turns out of contact with each other, the positionof the open binder structure in the assembly being such as positively tooppose and effectively to inhibit opening between the coherent wrappingturns during fiexion of the conductor, and the lead at which the lockingfilament is laid being so limited that the turns of the filament formwith the longitudinal axis of the conductor an angle sufilciently greateffectively to inhibit the tendency for the locking filament to breakwith loss of its locking effect on the turns of the wrapping upon severeflexion of the conductor.

5. An electrical conductor assembly comprising an electrically insulatedinner conductive structure and an outer protective jacket therefor inthe form of a helical serving of fibrous thread, having its turns laidclose together with a substantial lead and without overlap to givesubstantially complete coverage, in combination with an open lockingstructure of thread oppositely wound upon the jacket at a substantialangle with the conductor axis and with its turns so spaced as to exposethe greater part of said jacket, whereby the jacket is held intactdespite bending of the conductor assembly and the overall diameter fixedby the jacket is not materially increased by the locking structure.

WILLIAM C. ROBDISON. RALPH W. E. MOORE.

